Transition-metal- and organic-solvent-free: A highly efficient anaerobic process for selective oxidation of alcohols to aldehydes and ketones in water

Article abstract of DOI:10.1039/b509527a

A new system, I₂-KI-K₂CO₃-H₂O, selectively oxidized alcohols to aldehydes and ketones under anaerobic condition in water at 90°C with excellent yields. The process is green, mild and inexpensive. The Royal Society of Chemistry 2005.

Full text of DOI:10.1039/b509527a

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C O M M U N I C A T I O N
Transition-metal- and organic-solvent-free: a highly efficient
anaerobic process for selective oxidation of alcohols to aldehydes
and ketones in water†
Pranjal Gogoi and Dilip Konwar*
Organic Chemistry Division, Regional Research Laboratory, Jorhat, 785006, Assam, India.
E-mail: dkonwar@yahoo.co.uk
Received 12th July 2005, Accepted 17th August 2005
First published as an Advance Article on the web 1st September 2005
A new system, I2–KI–K2CO3–H2O, selectively oxidized al-
cohols to aldehydes and ketones under anaerobic condition
in water at 90 ◦C with excellent yields. The process is green,
mild and inexpensive.
imines to the corresponding aldehydes or ketones catalysed by
I2 in presence of a surfactant (SDS) in water.8
Herein, we want to report a new, efficient and an environ-
ment friendly system i.e. I2–KI–K2CO3–H2O for the selective
oxidation of alcohols to aldehydes and ketones in water. In a
typical experimental procedure, a mixture of alcohol, potassium
carbonate, iodine and a catalytic amount of potassium iodide,
dissolved in water, was stirred at 90 ◦C and after work-up
produced high to excellent yields of aldehydes and ketones.
Although the oxidation of alcohols with I2 in presence of base,
K2CO3 in water produced a trace amount of oxidized products,
the addition of a catalytic amount of KI in the reaction mixture
led to the formation of aldehyde and ketones at 90 ◦C with very
good to excellent yields (Scheme 1). The catalytic amount of
potassium iodide was optimised and 25 mol% was established
to be sufficient for the oxidation process.
In recent years, the search for environmentally benign chemical
processes or methodologies has received much attention from
chemists, because they are essential for the conservation of the
global eco-system.1 On the other hand, the selective oxidation
of alcohols to aldehydes and ketones is a pivotal transformation
in organic chemistry.2 In particular, the controlled oxidation of
primary alcohols to aldehydes, without forming over-oxidized
product is a challenging task for chemists. A number of oxidizing
methods using variety of reagents and conditions have been
developed, they involve transition metals,3 which are associ-
ated with waste disposal problems, use of oxygen-containing
oxidants4 and organic solvents2b,3a–f ,4b–f in the reaction mixture.
Also, despite the industrial importance of these processes and
ever growing environmental concerns, only a few efficient and
environmentally benign catalytic processes3d,3g,3j,5 are known till
today, which involve organic solvents, transition metals, O2–air,
O3, TEMPO etc. as the ultimate stoichiometric oxidants, and
this reaction awaits further development of high yielding, clean,
safe and inexpensive methods for the oxidation of alcohols. In
recent years, I2 has been used extensively as a synthetic reagent
due to its inherent properties of low toxicity, electrophilicity, and
easy handling.6 Recently, we described Brønsted acid catalysed
selective oxidation of alcohols to aldehydes and ketones using
DMSO as a nucleophilic oxidant, where the catalyst HI was gen-
erated in a redox process of N2H4 and I2 in hydrated acetonitrile.7
Very recently, we reported the deprotection of oximes and
Scheme 1 Oxidation of alcohols to aldehyde and ketones.
To investigate the scope and the general applicability of the
oxidation process under the optimised conditions, we examined
several different reagent systems (Table 1). Using these different
reagent systems the oxidation process successfully could be
performed. Among the systems under study, the system I2–KI–
K2CO3–H2O was the best, because it is efficient and cost effective
in comparison to the other systems. In a demonstration of the
practicality of this selected system (Table 1, entry 2), the oxida-
tion of 4-methoxybenzyl alcohol was carried out on a 13 g scale,9
the product (anisyldehyde) was isolated by fractional distillation
without using any chromatographic techniques with 95% yield.
† Electronic supplementary information (ESI) available: Experimental
details. See http://dx.doi.org/10.1039/b509527a
Table 1 Oxidation of 4-methoxybenzyl alcohol to anisyldehyde using different reagent systemsa
Entry
Reagent system
Time/min or h
Product
Yield (%)b
1c
2c
Na2CO3–NaI–I2–H2O
K2CO3–KI–I2–H2O
CsCO3–CsI–I2–H2O
K2CO3–I2–acetonitrile
K2CO3–KI–I2–acetonitrile
K2CO3–I2–acetone
20 min
20 min
18 min
1 h
1 h
1.5 h
6 h
1 h
1 h
2 h
p-Anisaldehyde
93
96
98
50
55
47
50
55
—
—
—
—
—
—
—
—
—
3c
4d
5d
6d
7e
K2CO3–I2–toluene
8d
CsCO3–I2–acetonitrile
Na2CO3–I2–acetonitrile
K2CO3–I2–H2O
9d
50
Trace
10c
a The reactions were carried out using 1 mmol of 4-methoxybenzyl alcohol with 1.5 mmol of base, 25 mol% of iodate and 1 mmol of iodine in 4 ml
water–organic solvent. b Isolated yield. c Stirred at 90 ◦C. d Stirred at refluxed temperature. e Stirred at room temperature.
T h i s j o u r n a l i s
T h e R o y a l S o c i e t y o f C h e m i s t r y 2 0 0 5
O r g . B i o m o l . C h e m . , 2 0 0 5 , 3 , 3 4 7 3 – 3 4 7 5
3 4 7 3
©

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Table 2 Anaerobic oxidation of alcohols to aldehyde and ketonesa
Entry
1
Substrate
Time/min
20
Product
Method
A
Yield (%)b
95
2
3
20
25
A
A
96
90
4
5
20
20
A
A
92
90
6
7
20
20
A
A
80
80
8
9
10
1-C7H15OH
1-C10H21OH
50
50
30
1-C6H13CHO
1-C9H19CHO
B
B
B
50
40
75
11
12
35
45
B
B
64
70
13
14
30
30
B
B
75
76
15
30
B
80
a Reaction conditions: alcohol (1 mmol), KI (25 mol%), I2 (1 mmol), 90 ◦C (oil bath temperature with magnetic stirring). Method A: K2CO3
(1.5 mmol), water (4 ml). Method B: K2CO3 (2 mmol), water (5 ml). b All the yields are pure and isolated products. c All the products are known and
compared with authentic data.13
The system was applicable for the oxidation of a wide variety
of primary and secondary alcohols to the corresponding aldehy-
des and ketones. During the oxidation of the alcoholic (primary
and secondary) group, the other functionality, such as ether,
nitro, halo, alkyl, aryl etc. survived intact under the oxidation
process. In this oxidation process, the aromatic primary alcoholic
groups (Table 2, entry 1–7) were oxidized with faster rate
and higher yields than the secondary aromatic/aliphatic and
primary aliphatic alcoholic (Table 2, entry 8–15) groups. In the
case of the cinnamyl (Table 2, entry 6) and furfuryl (Table 2,
entry 7) alcohols, the system produced neither cis nor trans
iodinated products during the oxidation process. This system
did not produced any a-iodinated aryl ketones in the case of
the secondary alcohols.10 On the other hand, this anaerobic
oxidation process is simply a subsequent deprotonation of
alcohols, therefore we did not get over-oxidized products of
3 4 7 4
O r g . B i o m o l . C h e m . , 2 0 0 5 , 3 , 3 4 7 3 – 3 4 7 5

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the primary alcohols i.e. acids during this oxidation process.
After separating the organic product layer from the reaction
mixture, the catalyst-cum-promoter, KI could be kept as such in
solution for further use or, the I2 may be regenerated by passing
O2 through the acidified inorganic end product.4b,11
(c) U. M. Lindstrom, Chem. Rev., 2002, 102, 2751; (d) S. Kobayashi
and K. Manabe, Acc. Chem. Res., 2002, 35, 209.
2 (a) M. Hudlicky, Oxidations in Organic Chemistry, American Chem-
ical Society, Washington, DC, 1990; (b) R. C. Larock, Comprehensive
Organic Transformation, A guide to functional group preparation,
VCH Publications, Inc., New York, 1989, p. 604-614.
Regarding the mechanism of the oxidation reaction, it is
proposed that the nucleophile alkoxide (formed by abstracting
acidic proton of alcoholic group by base) reacts with KI3
(generated in situ from I2 and KI),12 forms an intermediate state
A,10a which eliminates HI to generate aldehyde or ketones in the
reaction mixture, and finally the generated acid (HI) is being
scavenged by inorganic base to produce KI in water (Scheme 2).
3 (a) I. E. Marko, P. R. Giles, M. Tsukazaki, S. M. Brown and C. J.
Urch, Science, 1996, 274, 2044; (b) I. E. Marko, M. Tsukazaki,
P. R. Giles, M. S. Brown and C. J. Urch, Angew. Chem., Int. Ed.,
1997, 36, 2208; (c) B.-Z. Zhan, M. A. White, T.-K. Sham, J. A.
Pincock, R. J. Doucet, K. V. Ramana Rao, K. N. Robertson and
T. S. Cameron, J. Am. Chem. Soc., 2003, 125, 2195; (d) K. P. Peterson
and R. C. Larock, J. Org. Chem., 1998, 63, 3185; (e) S. S. Stahl,
J. L. Thorman, R. C. Nelson and M. A. Kozee, J. Am. Chem. Soc.,
2001, 123, 7188; (f) G.-J. ten Brink, I. W. C. E. Arends and R. A.
Sheldon, Science, 2000, 287, 1636; (g) D. R. Jensen, M. J. Schultz,
J. A. Mueller and M. S. Sigman, Angew. Chem., Int. Ed., 2003, 42,
3810; (h) M. Musawir, P. N. Davey, G. Kelly and I. V. Kozhevnikov,
Chem. Commun., 2003, 1414; (i) C. Li, P. Zheng, J. Li, H. Zhang, Y.
Cui, Q. Shao, X. Ji, J. Zhang, P. Zhao and Y. Xu, Angew. Chem., Int.
Ed., 2003, 42, 5063; (j) P. Gamez, I. W. C. E. Arends, J. Reedijk and
R. A. Sheldom, Chem. Commun., 2003, 2414.
4 For reviews of TEMPO–air–O2–DMSO–O3–NaOCl oxidized alco-
hol oxidations see: (a) W. Adam, C. R. Saha-Moller and P. A.
Ganeshpure, Chem. Rev., 2001, 101, 3499; (b) R. Liu, X. Liang,
C. Dong and X. Hu, J. Am. Chem. Soc., 2004, 126, 4112; (c) L. D.
Luna, G. Giacomelli and A. Porcheddu, J. Org. Chem., 2001, 66,
7907; (d) C. Bolm, A. S. Magnus and J. P. Hildebrand, Org. Lett.,
2000, 2, 1173; (e) P. L. Anelli, C. Biffi, F. Montanari and S. Quici,
J. Org. Chem., 1987, 52, 2559; (f) Z. R. Bright, C. R. Luyeye, A. S. M.
Morton, M. Sedenko, R. G. Landolt, M. J. Bronzi, K. M. Bohovic,
M. W. A. Gonser, T. E. Lapainis and W. H. Hendrickson, J. Org.
Chem., 2005, 70, 684.
Scheme 2 Proposed mechanism and tentative intermediates for the
anaerobic oxidation of alcohol.
In conclusion, we have discovered a highly efficient, mild
and inexpensive system that selectively oxidizes a wide range of
alcohols into aldehydes and ketones and it is free from oxygen-
containing oxidants, transition metals, and organic solvents
in the oxidation process. The system is applicable to a large-
scale production of aldehydes and ketones, and it is a green,
and economically viable anaerobic process for the oxidation of
alcohols to aldehydes and ketones.
5 H. Tohma, S. Takizawa, T. Maegawa and Y. Kita, Angew. Chem., Int.
Ed., 2000, 39, 1306.
6 L. A. Paquette, Encyclopedia of Reagents for Organic Synthesis, John
Wiley & Sons, New York, 1995, vol. 4, p.2796.
7 P. Gogoi, G. K. Sarma and D. Konwar, J. Org. Chem., 2004, 69,
5153.
Acknowledgements
8 P. Gogoi, P. Hazarika and D. Konwar, J. Org. Chem., 2005, 70, 1935.
9 The production of 4-methoxybenzaldehyde was carried out on a
∼13 g scale in 95% yield.
The authors acknowledge the Director, Dr P. G. Rao, the
Analytical Division of RRL, Jorhat, Assam, India, for their
help. Also, PG thanks CSIR, New Delhi for a grant of JRF
fellowship.
10 (a) J. Barluenga, M. Marco-Arias, F. Gonzalez-Bobes, A. Ballesteros
and J. M. Gonzalez, Chem. Commun., 2004, 2616; (b) S. Stavber, M.
Jereb and M. Zupan, Chem. Commun., 2002, 488.
11 J. D. Lee, Concise Inorganic Chemistry, ELBS edition of fourth
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